1. Field of the Invention
The present invention relates to a bearing apparatus which supports a rotating shaft for rotatably supporting a rotating member assembled in a casing.
2. Related Art Statement
A hydraulic pump is used to convert a rotational motion of an electric motor or the like into kinetic energy of a non-compressible fluid such as an oil, and a compressor is used to convert the motion into kinetic energy of a compressible fluid such as air.
Hydraulic pumps include a gear pump, a vane pump, a screw pump, and a radial piston pump. The gear pump is a pump which obtains a pumping effect by a movement of a volume surrounded by a tooth space and a casing and is divided into a circumscribed type and an inscribed type. A vane pump is a pump which obtains a pumping effect by a change of a volume defined between a plurality of vanes inserted in a groove of a rotor. A screw pump is a pump which moves forwards a fluid in an axial direction by rotating a shaft where a threaded surface is formed, and is divided into a one-shaft type, a two-shaft type, and a three-shaft type. An IMO type pump is known as a screw pump of the three-shaft type.
A piston pump is a pump of a type which suctions and discharges a liquid with use of a volume change caused by a reciprocal movement of a piston. An axial piston pump is equipped with a piston parallel to the axis of a cylinder block, while a radial piston pump is equipped with a piston arranged radially in a cylinder block.
As a compressor which use a compressible fluid such as air to obtain a compressed fluid of a predetermined value or higher, there is a compressor of a volume type. This type of compressor is divided into a rotation type which pressurizes a gas suctioned by rotation of a rotor in a casing like the vane type and the screw type of a hydraulic pump, and a reciprocation type which pressurizes a gas by a movement of a piston reciprocating in a cylinder. These hydraulic driving devices and air-pressure driving devices are described in, for example, KABUSHIKIKAISHA OHM-SHA, "SHINBAN YUATSU-BINRAN", pages from 204 and pages 445 to 451, Feb. 25, 1989.
A fluid-pressure driving device such as a pump or a compressor as described above have a rotor or a rotating member which is rotated and driven by a drive shaft connected to the motor. The rotor is brought into contact with a sliding surface such as a inner circumferential surface of the casing. If an unnecessarily excessive clearance is created between the casing and the rotor, the device cannot maintain its performance. If the rotor comes into collision with the inner surface, the device stops operating. Therefore, it is important to set a contact pressure and a pressure between the rotor and the inner surface to optimum values.
Thus, to manufacture a driving device such as a pump, the outer diameter of a rotor and the size of an inner circumferential surface of a casing must be processed to have predetermined precision, and how precisely respective components constituting the driving device can be processed is a significant point in view of maintaining performance of the device. It is therefore necessary to strictly manage tolerances of processing precision of respective components, and hence, problems occur in that the manufacturing steps are complicated and the manufacturing costs are increased.